Hydrocarbon-based fuels, for example, various petroleum fractions, heating oils, gasoline, diesel, kerosene, etc., generally contain numerous additives. Besides corrosion inhibitors and lubricity additives, these additives may include flow improvers or compounds which improve the emission levels of gases, such as CO, CO2 and/or NOx.
As a result of Directive 2003/30/EC, Article 3.1 (b), the European Parliament decreed that, effective Dec. 31, 2005, all diesel fuels should contain 2% biofuel. This percentage is supposed to increase to 5.75% by Dec. 31, 2010. In Article 2.2 of this Directive, biofuel is defined as bioethanol, rapeseed oil methyl ester (RSME), biogas, biomethanol, biodimethylether, biohydrogen, synthetic biofuels and purely vegetable oils.
In general, rapeseed oil methyl ester (RSME) is used as biodiesel. It is already possible that engines are being powered by pure biofuel under the EU Directive. However, it is likely that up to 2% RSME is being added to normal diesel in order to comply with the EU Directive.
This RSME is produced by converting the natural triglyceride into a methyl ester, or even an ethyl ester. The by-product of this process is crude glycerol. Because 100 kg free glycerol is formed in the production of 1 metric ton of RSME as biodiesel, the amount of glycerol available increases with the increasing production of RSME. Since there is a limited market for glycerol, which market is already satisfied by existing production, glycerol disposal problems arise. This situation makes the normal production route economically unattractive and potentially limits the use of this route for producing biodiesel, as glycerol can no longer be factored in as additional profit.
Glycerol has to be removed from the diesel and biodiesel being produced, as a high glycerol level adversely affects the combustion performance of those fuels. One reason for this is the poor solubility of glycerol in the rapeseed oil methyl ester generally used as biodiesel. An excessive concentration of glycerol in the methyl ester leads to the formation of a heavy glycerol phase, which can settle, for example, in the fuel tank. If such a glycerol phase is injected into the engine, performance is reduced, and the wear on individual engine components is potentially increased.
Various enzymatic routes suitable for the production of monoglycerides have been described in the literature, including: 1) enzymatic synthesis starting from fatty acid and glycerol; 2) enzymatic glycerolysis starting from triglyceride and glycerol, which corresponds to the chemical process; and 3) the 1,3-regioselective hydrolysis or alcoholysis of triglyceride. Summaries of these processes may be found, for example, in Recent Res. Devel. Oil Chem., 3 (1999), 93-106; and Hydrolases in Organic Synthesis, Wiley-VCH (1999), eds. Bornscheuer & Kazlaukas.
Enzymes increasingly are being used as catalysts in chemical and biochemical syntheses. Thus, in many cases, hydrolases, more especially lipases (EC 3.1.1.3), are already being used for lipolysis or transesterification in industrial processes by virtue of the often relatively mild reaction conditions. These enzymes are produced by various microorganisms, then to isolate them, fermentation of the microorganisms is followed by an expensive purification process. The effectiveness of these catalysts is often offset by the high costs of production and isolation, driving research groups to constantly strive to increase the yields of these enzymes and/or the productivity of them. The standard chemical method for producing monoglycerides involves the base-catalyzed glycerolysis of triglycerides, a yield of 40 to 60% monoglyceride, based on the total glycerides, typically being obtained. Further enrichment to a >90% monoglyceride content is achieved by physical separation techniques, such as molecular distillation or crystallization.
WO 90/13656 and WO 90/04033 (both Enzytech, Inc.) and U.S. Pat. No. 5,935,828 and U.S. Pat. No. 5,316,927 (both Zaks et al.) describe the production of monoglycerides by enzymatic alcoholysis with various alcohols and a little water in the mixture. Lipases are used in powder form or are immobilized. In the Examples, the alcohol component is present in a 20-fold excess, and lipases are used in quantities of ca. 20%, by weight, based on the triglyceride.
WO 91/16441, WO 91/16442 (both Procter & Gamble) and U.S. Pat. No. 5,116,745 (Mazur et al.) describe processes in which a mixed regioselective alcoholysis and hydrolysis to 1,2-diglycerides and 2-monoglycerides, using lipases, is carried out in the presence of a solvent, an alcohol and an aqueous buffer.
EP 0 407 959 A2 (Lion Corporation) describes a process for the production of monoester using a thermostable, immobilized lipase in the presence of secondary or tertiary alcohols as solubilizers.
WO 02/06505 A1 (Nippon Suisan Kaisha Ltd.) describes regioselective alcoholysis using an immobilized lipase, a large excess of alcohol and high concentrations of enzyme, followed by re-esterification of the monoglyceride.
JP 03108489 and JP03187385 (Meito Sangyo Co. Ltd.) describe the regioselective hydrolysis of triglycerides with an alkaline lipase in the presence of alkaline salts. The lipase used is only active under alkaline conditions.
JP 03103499 (Meito Sangyo Co. Ltd.) describes the regioselective alcoholysis of PUFA triglycerides with isobutanol in the presence of an alkaline lipase.
Although the enzymatic production of partial glycerides has already been widely described, solvents are required in all the above-cited documents, the water of reaction has to be removed at considerable expense, and the special lipases are used that are not commercially available on an industrial scale.
Now, a first objective of this invention was to provide a biofuel which would comply with the guidelines of the European Parliament and in which the glycerol would be present as a derivative, resulting in very little free glycerol being formed as a by-product in the production process. Thus, the production process would be environmentally friendly and economical. A second objective of this invention was to find an inexpensive enzymatic or chemical variant that would increase the yield of monoglycerides and diglycerides from polyol esters, such as triglycerides, for example, and where the enzyme content in the enzymatic alcoholyses would be kept to a minimum.